Sheet parameter measurement

ABSTRACT

A measuring device useful for measuring mechanical properties of highly flexible or limp sheet materials. The device includes a base, a pair of clamping members, with one of the clamping members being movable away from and toward the second clamping member. A load sensor is mounted in one of the clamping means for measuring of the required mechanical properties.

[0001] This invention relates to the measurement of the mechanicalproperties of highly flexible or limp sheet material, for example paper,textile material, plastics and composite materials. In particular, theinvention relates to the measurement of the tensile, shear, buckling,and compression strengths, sheet thickness, bending stiffness andsurface qualities such as friction and roughness. The purpose of suchtesting, under normal loading without destruction of the sample of thematerial under test, is to determine the performance of the material inuse, e.g. clothing fabrics during normal wear.

[0002] To date, such measurements have generally been made independentlyon different samples of the material to be tested. For example, there isthe widely accepted Kawabata Evaluation System for Fabric (KESF) fortextile fabrics. With this system, different samples of the fabric to betested are required to be placed in several different devices in orderto make the measurements of the various properties listed above. Onesample of the fabric to be tested is placed in a device which measurestensile and shear properties by clamping the sample at two spacedlocations and moving the clamps apart and laterally relative to eachother. This device has to be calibrated for each measurement on asample. Bending strength, but not buckling, is measured by placing adifferent sample of the fabric in a second device. In this device thesample is mounted vertically and the device is very difficult to set upin trying to achieve an even tension in the fabric. One clamp makes acircumferential movement in order to measure the bending strength.Thickness measurement requires another measuring device. In this case ahead moves vertically relative to the fabric in order to measure thethickness of the material and then its compressibility. For surfaceproperties, a further sample of the material is clamped under load in afurther device in which a head lowers and the material is then movedlaterally relative to the head. Different probes on the head measuresurface roughness and friction. It is very expensive to have all ofthese devices and very time consuming to place the different samples inthe different devices in order to make all of the measurements. Anothersystem is the Fabric Assurance by Simple Testing (FAST) system.

[0003] This is a simplified version of the KESF system, but at least twodifferent samples are needed.

[0004] Thickness and compression are measured in one device at twopositions of a movable head.

[0005] Bending is measured in another device in which the fabric is laidon a bed and is traversed by a moving plate on top of the fabric untilthe fabric extends over the edge of the bed and cuts a light beam. Fortensile strength, the fabric is placed between two clamps in a furtherdevice, the lower one of the clamps being on an arm which is pivoted andhas a weight on the other end. When the arm is released, the deviceregisters the load in the fabric. The results from these tests arelimited to the measured loads only and cannot provide full stress/strainprofiles of the test samples. In addition the results from the two testsystems are not very reproducible, due to the need for different samplesizes and the manual handling for each test. In the cosmetics andmedical fields it is desirable to determine the effect cosmetic ormedical creams and the like have on the human skin. To this end a fabricwhich has similar characteristics to human or animal skin is treatedwith the cream and the mechanical properties of fabric are thenmeasured. For such an application the KESF and FAST systems areconsidered too expensive and too complicated.

[0006] It is an object of the present invention to provide a singleapparatus for the measurement of the mechanical properties of a singlesample of a limp sheet material in order to reduce the equipment costscompared with that of the number of existing devices required. It isalso an object of the present invention to reduce the time andcomplexity of making such measurements and to increase the accuracy andreproducibility of such measurements compared with the existing methods.

[0007] The invention provides a device for the measurement of themechanical properties of a limp sheet material, comprising a base, apair of clamping members operable to clamp the sheet material to thebase at spaced locations, load sensing means on at least one clampingmember, at least one of the clamping members being movable away from andtowards the other in the plane of the sheet material and laterally ofthe other in said plane, and a head assembly having a sensing devicespaced from the base and movable theretowards and laterally of the planeof the sheet material.

[0008] One clamping member may be the at least one movable clampingmember and the load sensing means may be mounted on the other clampingmember. Two load sensing means having differing ranges of measurementmay be mounted on the one clamping member, the first load sensing meansbeing adapted to measure tensile load and the second load sensing meansbeing adapted to measure buckling load. The measurement device maycomprise a third load sensing means adapted to measure shear loads. Thesensing device may comprise a further load sensing means and a surfacecharacteristics sensing means.

[0009] Preferably the base is a plate which is disposed substantiallyhorizontally, in which case the clamping members may be disposed abovethe base plate and positionally adjustable to clamp the sheet material.The measuring device may comprise position indicating means adapted toindicate the position of the at least one movable clamping memberrelative to a datum position. The at least one movable clamping membermay be mounted on low friction slideways, and the slideways may bedisposed remote from the axes of movement of the at least one movableclamping member. The head assembly may be disposed between the clampingmembers, and may be mounted on the base plate. The head assembly maycomprise a slide part on which the sensing device is mounted formovement towards the base plate and, together with the slide part,laterally of the sheet material.

[0010] The base plate may have an edge to a side of the at least onemovable clamping member remote from the other clamping member, overwhich edge the sheet material may be moved to cantilever thereover. Themeasurement device may comprise a beam transmitting device and a beamsensing device operable to receive the transmitted beam and detect whenthe sheet material interrupts the beam. The beam may be directed frombeneath and spaced from the edge of the base plate at an angle ofbetween 30° and 60° to the horizontal.

[0011] Preferably the beam is directed at an angle of 41.5° to thehorizontal. The base plate may be formed to have a shallow recessbetween the spaced locations to reduce the frictional contact betweenthe sheet material and the base plate.

[0012] The measurement device may comprise control means operable tocontrol the sequence of movement of the at least one movable clampingmember and the sensing device. The control means may also be operable torender operable the first or second load sensing means for measuringtensile load or buckling load respectively dependent on the direction ofmovement from the datum position of the at least one movable clampingmember. The control means may be operable to vary the length of timebetween successive movements of the at least one movable clamping memberand the sensing device. The control means may also be operable to adjustthe speed of movement of the at least one movable clamping member andthe sensing device. The control means may comprise programmable meansfor the selection of the measurements to be made, the speed of movementof the at least one movable clamping member and the sensing device, andthe timing of the movements.

[0013] The movement of the at least one movable clamping member and thesensing device may be effected by respective stepper motors. Theclamping members may also be moved between respective sample materialrelease positions and their clamping positions by respective steppermotors.

[0014] In another aspect, the invention relates to methods and apparatusfor the assessment of seam pucker and other surface irregularities.

[0015] Assessment of surface irregularities, particularly seam pucker,is at present largely a subjective matter. Attempts to introduceobjectivity into the assessment have, to date, not been so successful asthe result is non-standard. The same is true for measurements,generally, of surface irregularities of which seam pucker istypical—with the exception, possibly, of microscopic surface roughnessmeasurements, necessarily automated and standardized because ofinaccessibility to the naked eye—surface irregularity is “judged” ratherthan objectively measured.

[0016] The invention provides an objective assessment for seam puckerand other, comparable surface irregularities.

[0017] The invention comprises a method for the assessment of seampucker and other surface irregularities comprising directing at thesurface a line beam from an illuminator, imaging the line on the surfaceformed by the line beam and analysing data of the image to produce anobjective indication of the degree of irregularity of the surface.

[0018] Parallel line beams may be directed at the surface. For theassessment of seam pucker, the parallel line beams may be directed toform lines on the surface parallel to and either side of the seam, andat an angle from the plane perpendicular to the surface.

[0019] The illuminator may comprise a line beam laser.

[0020] The line on the surface may be imaged by a pixel image such as aCCD array camera.

[0021] The image may be analysed in a computer programmed with imageanalysis software. The result of analysing the image may be a display ofa distribution of severity of deviation of the surface from flat.

[0022] The surface may be that of a limp material, such as a textilefabric, mounted on a flat support base. The base may, for theassessment, be inclined steeply with the material clamped uppermost andresting against the base below the clamping location.

[0023] For consistency of measurement the material is preferably thesame size as the bed, so no additional irregularity is occasioned byedge effects. A sample for assessment may be cut to size using the bedas a template.

[0024] The invention also comprises surface irregularity assessmentapparatus comprising

[0025] a line beam illuminator;

[0026] a support arrangement for the surface under assessment such thatthe line beam illuminator is directed at the surface to illuminate aline thereon;

[0027] an imaging arrangement adapted to image the line illuminated onthe surface, by the line beam illuminator; and

[0028] analysis means adapted to receive image data to produce anobjective indication of the degree of irregularity of the surface.

[0029] There may be one, two or more line beam illuminators castingparallel beams. Beams may be cast in different arrangements to providefurther information.

[0030] The imaging arrangement may comprise a pixel imaging arrangement,and may comprise a CCD array.

[0031] The line illuminator may be a laser.

[0032] The analysis means may comprise a computer programmed with imageanalysis software.

[0033] Embodiments of the invention will now be further described withreferences to the accompanying drawings in which:

[0034]FIG. 1 is a front elevation,

[0035]FIG. 2 is a view on line 2-2 of FIG. 1,

[0036]FIG. 3 is a perspective view of an apparatus for measuring seampucker, in simplified form;

[0037]FIG. 4 is a view of an illuminated sample in the apparatus of FIG.3; and

[0038]FIG. 5 is a block diagram of the apparatus of FIG. 3.

[0039] Referring now to FIGS. 1 and 2, there is shown a measurementdevice 10 comprising a substantially horizontally disposed base plate 11on which a sample 12 of the material to be tested is placed. A ‘fixed’clamping member 13 and a ‘movable’ clamping member 14 are mounted onrespective supports 15, 16 and are movable by respective stepper motors17, 18 from their respective sample material release positions as showndownwardly towards the base plate 11 to clamp the sample 12. At thisinitial stage the ‘movable’ clamping member 14 and its ‘movable’ support16 are in the ‘datum position and the end of the sample 12 is alignedwith the end 19 of the base plate 11. Mounted on a head support 20 is ahead assembly comprising a slide part 20 a which is movable by means ofstepper motor 21 and lead screw laterally of the sample 12 in slideways22 and a sensing part 20 b which is movable by means of a stepper motor23 vertically in slideways 24. The sensing part 20 b has a sensingdevice 25 which incorporates load sensing means 26 and a surfacecharacteristics sensing means 27. A position sensor 28 is provided onthe support 20 to measure the height of the head assembly 20 relative tothe base plate 11.

[0040] The ‘movable’ support 16 is mounted on the base plate 11 in lowfriction slideways 29 disposed remote from the axis 30 of movement ofthe ‘movable’ support 16 to minimise the effects of friction on theoperation and measurement sensitivity of the measurement device 10. The‘movable’ support 16 is movable by means of stepper motor 31 and leadscrew 32 away from and towards the ‘fixed’ support 15, and a positionsensor 33 indicates the position of the ‘movable’ support 16 relative toa datum position. The upper part 16 a of the ‘movable’ support 16 ismovable in slideways 34 in lower part 16 b by stepper motor 35 laterallyof the base plate 11. A position sensor 36 indicates the lateralposition of the ‘movable’ support 16 relative to a datum centralposition. In fact, the ‘fixed’ support 15 is also mounted on theslideways 29 and is movable from its datum position 16 under the effectof a change in the tension in the sample 12. Any such change in tensionis detected by load cells 37, 38. The ‘movable’ support 16 may beextended as shown to support the sample 12 when it is moved towards theedge 19 of the base plate 12 for the bending test described below.

[0041] Located adjacent the edge 19 of the base plate 12 is a beamtransmitting device 39 and a beam sensing device 40 operable to receivethe transmitted beam 41 and detect when the sample 12 interrupts thebeam 41. The beam transmitting device 39 is mounted at the edge 19 andthe beam 41 is directed downwardly towards the base plate 11 at an angleof 41.5° to the horizontal.

[0042] A control device 42, including programmable means 43 is providedto control automatically the operation of the measuring device 10, whichis as follows. The prepared sample 12 of the material to be tested isplaced in the measuring device 10 on the base plate 11 so that the endof the sample aligns with the edge 19 of the base plate 11. The controldevice 42 is activated and the clamping members 13, 14 are lowered bytheir motors 17, 18 to clamp the sample 12. Load cell 37, having a rangeof measurement appropriate to the measurement of tension in the sample12 is brought into operation by the control means 42 and the other loadcell 38 is taken out of operation. The motor 31 is then operated to movethe ‘movable’ support 16 from its datum position in a direction awayfrom the ‘fixed’ support 15. This movement applies a tensile load to thesample 12, which is measured by the load cell 37. A shallow recess 44 inthe base plate 11 under the sample 12 reduces the effect of frictionbetween the sample 12 and the base plate 11. The distance moved by the‘movable’ support 16 is measured by the position sensor 33, so that a‘load-extension’ relationship for the sample 12 can be determined. Thecontrol means 42 reverses the motor 31 to return the ‘movable’ support16 to its datum position. The load sensor 37 is taken out of operationand the load cell 38, having a range of measurement appropriate to themeasurement of buckling load in the sample 12, is brought intooperation. Further movement of the ‘movable’ support 16 towards the‘fixed’ support 15 enables the load in the sample 12 as it buckles to bemeasured by the load cell 38. The ‘movable support 16 is then againreturned to its datum position.

[0043] The sensing part 20 b of the head support 20 is then lowered bymeans of the motor 23 until contact between the sample 12 and thesurface characteristics sensing means 27. The height of the surfacecharacteristics sensing means 27 above the base plate 11 is indicated bythe position sensor 28 so as to determine the thickness of the sample12. Further lowering of the sensing part 20 b will apply a compressiveload to the sample 12, as determined by the load cell 26. Correlation ofthe readings of the load cell 26 and the position sensor 28 will providea ‘Load-compression’ relationship for the sample 12. The sensing part 20b is then raised to the position of contact between the sample 12 andthe surface characteristics sensing means 27. Lateral movement of theslide part 20 a along slideways 22 by means of motor 21 causes thesurface characteristics sensing means 27 to measure the friction betweenit and the sample 12 and also the surface roughness of the sample 12.The sensing part 20 b is then raised to its original position.

[0044] The control means 42 then activates motor 36 to move the upperpart 16 a of the ‘movable’ support 16 laterally of the base plate 11.This induces a shear in the sample 12, and the shear load is indicatedby a further load cell 45. Correlation of the readings of the load cell45 and the position sensor 36 will provide a ‘Load-shear’ relationshipfor the sample 12.

[0045] To determine the bending characteristics of the sample 12, thecontrol means 42 now activates motors 17 and 18 to raise the ‘fixed’ and‘movable’ clamping members 13, 14 to release the sample 12. Motor 31 isthen activated to move the ‘movable’ support 16 and the sample 12 awayfrom the ‘fixed’ support 15. During this movement the sample 12 issupported by the extended support 16 c. This causes the end of thesample 12 to cantilever over the edge 19 of the base plate 11,eventually to bend and hang downwardly 50 as to interrupt the beam 41.The position sensor 33 indicates the amount of sample 12 extending overthe edge 19 of the base plate 11 when the beam 41 is interrupted, thisamount being dependent on the stiffness of the material of the sample12.

[0046] If not all of the above measurements are required, suitableprogramming of the programmable means 43 can cause the control means 42only to activate the relevant motors for the measuring device to performthe required operations. Furthermore, if the effect of the speed ofapplication of any load to the sample 12 is required, the programmablemeans 43 can be programmed to alter the speed of operation of therelevant motor or motors. As a further benefit of the measuring device10, cyclic loading of the sample 12 may be effected by suitableprogramming of the programmable means 43.

[0047] Alternative embodiments of measuring device according to theinvention will be apparent to persons skilled in the art. For example,as an alternative to stepper motors, the movements of the movable partsof the measurement device may be effected by pneumatic or hydrauliccylinders or by linear motors. As another alternative construction, theslide and sensing parts 20 a, 20 b may be mounted on the upper part 16 aof the ‘movable’ support 16. By means of the present inventionmeasurements of tensile, shear, buckling, and compression strengths,sheet thickness, bending stiffness and surface qualities such asfriction and roughness can be made on a single sample of a limp sheetmaterial in a single measuring device, thereby reducing the timeinvolved in performing the tests and the initial cost of purchasing thenecessary equipment.

[0048] FIGS. 3 to 5 of the drawings illustrate a fabric sample 311 witha seam 312 giving rise to seam pucker—undulations 13 in the fabriceither side of the seam 312—held by a clamp 314 on a support base 315inclined steeply so the fabric rests on the base rather than hangsfreely, but otherwise without any constriction that would give rise tospecious undulation or flattening and of any pucker that might bepresent. A bridge 315 a on the support base 315 restricts movement ofthe sample 311 during monitoring.

[0049] The base 315 is removable from an enclosure in which theassessment is carried out and may be used as a template in cutting asample for assessment from a larger piece.

[0050] Two parallel line beam lasers 316, 317 are directed at the sample311 so that they illuminate lines 318 either side of the seam 312.

[0051] As seen in FIG. 4, these lines take on a undulating appearancebecause of the seam pucker. The sample is imaged by a CCD camera 319,which is arranged at such a distance from the sample that thedistortions due to seam pucker in the lines 318 are visible in theimage.

[0052] The whole is enclosed, for the assessment, in a box, and should,to prevent laser light escaping that might damage eyes be vieweddirectly, there being an interlock arrangement to ensure the laserscannot operate unless the box is closed.

[0053] The image from the camera 319 is fed to a computer 321, FIG. 5,with a vision card 322 and software capable of analysing the image bysuitable routines to assess the degree and spatial frequency of anyundulation caused by seam pucker.

[0054] Clearly a similar set-up can be employed to assess other types ofsurface irregularity.

[0055] The apparatus may readily be miniaturized and presented as ahand-held arrangement for portable use.

1. A device for the measurement of the mechanical properties of a limpsheet material, comprising a base, a pair of clamping members operableto clamp the sheet material to the base at spaced locations, loadsensing means on at least one clamping member, at least one of theclamping members being movable away from and towards the other in theplane of the sheet material and laterally of the other in said plane,and a head assembly having a sensing device spaced from the base andmovable theretowards and laterally of the plane of the sheet material.2. A measurement device according to claim 1, wherein one clampingmember is the at least one movable clamping member and the load sensingmeans is mounted on the other clamping member.
 3. A measurement deviceaccording to claim 2, wherein two load sensing means having differingranges of measurement are mounted on the other clamping member.
 4. Ameasurement device according to claim 3, wherein a first one of the loadsensing means is adapted to measure tensile load and a second one of theload sensing means is adapted to measure buckling load.
 5. A measurementdevice according to claim 4, comprising a third load sensing meansadapted to measure shear loads.
 6. A measurement device according to anyone of claims 1 to 5, wherein the sensing device comprises a furtherload sensing means and a surface characteristics sensing means.
 7. Ameasurement device according to any one of claims 1 to 6, wherein thebase is a plate which is disposed substantially horizontally.
 8. Ameasurement device according to claim 7, wherein the clamping membersare disposed above the base plate and are positionally adjustable toclamp the sheet material.
 9. A measurement device according to any oneof claims 1 to 8, comprising position indicating means adapted toindicate the position of the at least one movable clamping memberrelative to a datum position.
 10. A measurement device according to anyone of claims 1 to 9, wherein the at least one movable clamping memberis mounted on low friction slideways
 11. A measurement device accordingto claim 1, wherein the slideways are disposed remote from the axes ofmovement of the at least one movable clamping member.
 12. A measurementdevice according to any one of claims 1 to 11, wherein the head assemblyis disposed between the clamping members.
 13. A measurement deviceaccording to claim 12, wherein the head assembly is mounted on the baseplate.
 14. A measurement device according to claim 13, wherein the headassembly comprises a slide on which the sensing device is mounted formovement towards the base plate and laterally of the sheet material. 15.A measurement device according to any one of claims 1 to 14, wherein thebase plate has an edge to a side of the at least one movable clampingmember remote from the other clamping member, over which edge the sheetmaterial may be moved to overhang therefrom.
 16. A measurement deviceaccording to claim 15, comprising a beam transmitting device and a beamsensing device operable to receive the transmitted beam and detect whenthe sheet material interrupts the beam.
 17. A measurement deviceaccording to claim 16, wherein the beam is directed from the beamtransmitting device adjacent the edge of the base plate at an angle ofbetween 30° and 60° to the horizontal.
 18. A measurement deviceaccording to claim 171 wherein the beam is directed at an angle of 41.5°to the horizontal.
 19. A measurement device according to any one ofclaims 1 to 18, wherein the base plate is formed to have a shallowrecess between the spaced locations to reduce the frictional contactbetween the sheet material and the base plate.
 20. A measurement deviceaccording to any one of claims 1 to 19, comprising control meansoperable to control the sequence of movement of the at least one movableclamping member and the sensing device.
 21. A measurement deviceaccording to claim 20 when dependent on claim 4, wherein the controlmeans is operable to render operable the first or second load sensingmeans for measuring tensile load or buckling load respectively dependenton the direction of movement from the datum position of the at least onemovable clamping member.
 22. A measurement device according to claim 20or claim 21, wherein the control means is operable to vary the length oftime between successive movements of the at least one movable clampingmember and the sensing device.
 23. A measurement device according to anyone of claims 20 to 22, wherein the control means is operable to adjustthe speed of movement of the at least one movable clamping member andthe sensing device.
 24. A measurement device according to claim 23,wherein the control means comprises programmable means for the selectionof the measurements to be made, the speed of movement of the at leastone movable clamping member and the sensing device, and the timing ofthe movements.
 25. A measurement device according to any one of claims 1to 24, wherein the movement of the at least one movable clamping memberand the sensing device is effected by respective stepper motors.
 26. Ameasurement device according to claim 25, wherein the clamping membersare moved between respective sample material release positions and theirclamping positions by respective stepper motors.
 27. A method for theassessment of seam pucker and other surface irregularities comprisingdirecting at the surface a line beam from an illuminator, imaging theline on the surface formed by the line beam and analysing data of theimage to produce an objective indication of the degree of irregularityof the surface.
 28. A method according to claim 27, in which parallelline beams are directed at the surface.
 29. A method according to claim28, for the assessment of seam pucker, in which the parallel line beamsare directed to form lines on the surface parallel to and either side ofthe seam, and at an angle from a plane perpendicular to the surface. 30.A method according to any one of claims 27 to 29, in which theilluminator comprises a line beam laser.
 31. A method according to anyone of claims 27 to 30, in which the line on the surface is imaged by apixel imager such as a CCD array camera.
 32. A method according to anyone of claims 27 to 31, in which the image is analysed in a computerprogrammed with image analysis software.
 33. A method according to anyone of claims 27 to 32, in which the result of analysing the image is adisplay of a distribution of severity of deviation of the surface fromflat.
 34. A method according to any one of claims 29 to 33, in which thesurface is of a limp material such as a textile fabric mounted on a flatsupport bed.
 35. A method according to claim 34, in which the flatsupport bed is, for the assessment, inclined steeply with the materialclamped uppermost and resting against the bed below the clampinglocation.
 36. A method according to claim 34 or claim 35, in which thematerial is the same size as the bed.
 37. A method according to claim36, in which the material is cut to size using the bed as a template.38. Surface irregularity assessment apparatus comprising: a line beamilluminator; a support arrangement for the surface under assessment suchthat the line beam illuminator is directed at the surface to illuminatea line thereon; an imaging arrangement adapted to image the lineilluminator on the surface by the line beam illuminator; and analysismeans adapted to receive image data to produce an objective indicationof the degree of irregularity of the surface.
 39. Apparatus according toclaim 38, in which there are one, two or more line beam illuminatorscasting parallel beams.
 40. Apparatus according to claim 38 or claim 39,in which the imaging arrangement comprises a pixel imaging arrangement.41. Apparatus according to claim 40, in which the pixel imagingarrangement comprise a CCD array.
 42. Apparatus according to any one ofclaims 38 to 41, in which the line illuminator and the imagingarrangement point at the surface from different directions. 43.Apparatus according to any one of claims 38 to 42, in which the lineilluminator is a laster.
 44. Apparatus according to any one of claims 38to 43, in which the analysis means comprises a computer programmed withimage analysis software.